1. Field of the Invention
This invention relates to life support systems equipment, and, more particularly, to an equipment array utilizing an improved Bernoulli effect tube arrangement to reduce exhalation pressure on the user while saving his exhaled gas for reuse after "scrubbing" out its carbon dioxide (CO.sub.2) contaminants.
Sport diving, fishing, oil rig maintenance and a variety of land search and rescue operations, in contaminated environments, require a person to carry his own supply of breathable gas into a hostile environment of operation. Present day systems generally rely on bulky cylinders of breathable gas with manually controlled supply valves which require constant attention from the user, and these systems are of such a nature that the exhaled gas of the user is exhausted directly from the lungs of the user into the adjacent environment, severely limiting "stay time" in that environment through the mass and bulk limits of stored breathable gas capable of being carried by him.
The device herein described will be presented in a discussion utilizing compressed air as the breathable gas being considered, but combinations of pure oxygen, oxygen/helium or oxygen augmented air are suitable substitutes wherever "breathable gas" is used in the discussion. It provides for safe, more efficient use of the "fresh" breathable gas by having it act as a forcing means to pull exhaled gas through a CO.sub.2 filter rendering the residual oxygen of that exhaled gas useable by the system operator when it is enriched with fresh breathables. As a direct consequence of this use of exhaled gas, stay time in the operational environment is greatly extended for a given quantity of stored, fresh, breathable gas.
2. Description of the Prior Art.
Nominal composition of air at sea level and under standard atmospheric conditions is approximately 20% oxygen and 80% inert gases or elements not useable in the body's metabolic processes. Upon inhalation, air passes through a person's lungs, oxygenating the body's blood supply for transport of that oxygen to the organs and tissues requiring the blood's nutrients and oxygen. Exhalation of the air breathed produces a mixture in which approximately 20% of the original oxygen of the air has been converted to carbon dioxide so that this exhausted air's composition is roughly 4% carbon dioxide, 80% inert elements and 16% oxygen.
Since oxygen is the component required for the body's metabolic processes, this exhaust air has considerable metabolic value remaining and so has corresponding value to the user. As described in U.S. Pat. Nos. 3,016,053 and 3,021,839, certain systems have been designed to salvage this useable oxygen in rebreathable gas storage systems and the invention described herein provides significant improvement over such systems.
The rebreathable gas storage systems of the referenced patents operate in a semi closed circuit arrangement wherein the user exhales directly into a CO.sub.2 scrubber which removes that contaminant and passes the purefied mixture to a storage reservoir. Pressure used to force the gas through the scrubber is provided by the user in muscular contraction of his chest and so forcing flow of the mixture from his lungs through the scrubber and into the reservoir. From the storage reservoir, the rebreathed gas is enriched with higher oxygen content unused or "fresh" breathable gas from a storage source, breathed by the user, and the cycle repeated.
Typical SCUBA (self contained underwater breathing apparatus) systems employ stored breathables in high compression cylinders carried by the diver or user. With standard manual control valves, the diver can set the pressure of his first stage regulator and manually open or close the stored breathables supply to breathing parts of his equipment. In use, his inhalation provides breathables through a check valve and, upon satisfaction of his oxygen intake requirements, the diver exhales through a second check valve, exhausting the breathed gases into the surrounding environment. This type of system is known as an "open circuit"0 system, where there is no circulation of gases. Breathables are consumed from the supply and exhausted directly into the surrounding environment. This same type of breathing system is used in surface rescue systems employing different types of breathing ports, face masks, etc. It is well recognized that while the open circuit system is the safest and simplest of breathable gas systems, it is also the most inefficient, in that approximately 80% of the oxygen value in the stored breathables is wasted upon its exhaust to the ambient environment. (Reference U.S. Pat. No. 3,021,839, column 1, lines 29 through 49)
Advantages and disadvantages of closed circuit systems fully utilizing the breathed gases of the user are described in the referenced patents as well as the "semi-closed circuit" system proposed as the invention therein.
The within invention incorporates the efficiencies of the above "semi closed circuit" system by recirculation of breathed gases for salvage of their high oxygen content, but improves significantly thereon by using the flow of high pressure fresh breathables to boost the recirculated gas through its treatment apparatus, (actually a CO.sub.2 filter or absorbent purifier) relieving the user from the task of forcing the breathed gases through it with his lung power on exhalation. The invention operates in what is described as "semi open circuit" mode because the user exhausts his lungs into a receiver which is at the pressure of the outside environment, much as in the open circuit mode, but he preserves the exhalation gases for reuse, exhausting the excess to the environment. (The "excess" being that amount of breathed gas not pulled through the treatment apparatus. This amount, or fraction, in turn, being determined by design of the jet and breathing tube described in the attached specification.)
Novelty and utility of the device proposed herein rest in its ability to provide energy from the stored supply of fresh breathable gas to "force" exhaled gas through a CO.sub.2 scrubber/filter for reuse by the system operator with augmentation of that exhaled and purified gas by fresh breathable material from the "forcing" gas itself. The energy used for pulling exhaled gas through the scrubber/filter is so supplied by the oxygen enriching supply gas of the system rather than by lungs and muscles of the user as in other life support systems utilizing rebreathable gas.